Agricultural vehicles such as tractors often are attached to one or more driven devices that require power in order to operate. Such devices may include equipment or implements such as mowers and spreaders. Commonly, the agricultural vehicles provide power to these attached devices by way of power take-off shafts (PTOs). These PTOs allow rotational power to be transmitted from the agricultural vehicles to the attached devices when input (or implement) shafts of the attached devices are coupled to the PTOs.
As the use of PTOs developed, most tractor manufacturers standardized on operating PTOs at either 540 RPM or 1000 RPM. In addition, manufacturers standardized the sizes (particularly the diameters and lengths) of PTOs and standardized the output spline arrangements of PTOs. (The output splines along the PTOs provide the transfer of torque between the PTOs and the input shafts of the attached devices and determine whether a particular attached device may be attached to a particular PTO.) Three PTO standards that are of interest because of their common implementation on tractors are (1) a 13/8" PTO operating at 540 RPM, (2) a 13/8" PTO operating at 1000 RPM, and (3) a 13/4" PTO operating at 1000 RPM (where 13/8" and 13/4" refer to the diameter of that portion of a PTO where the PTO interfaces an attached device).
While earlier agricultural vehicles only provided a single PTO (e.g., a 13/8" PTO operating 540 RPM), recent agricultural vehicles have flexible PTO output systems that allow the vehicles to provide multiple PTOs. For example, a tractor may have two or more PTOs, each at a different PTO standard. Implements configured to receive power at the different PTO standards may be attached to their respective matching PTOs. (Typically, only one device would be attached at a time since simultaneous attachment of more than one device would tend to overload the tractor engine.) Therefore, operators of such agricultural vehicles have the option of attaching a variety of devices to the agricultural vehicles even though the devices themselves are designed to receive power by way of PTOs in only one (or another) of the various PTO standards.
One known flexible PTO output system employs interchangeable and removable PTOs. PTOs for operation at the three above-mentioned PTO standards (or other standards) are each designed to fit within the same PTO port on the agricultural vehicle. The PTO port may include an output sleeve (i.e., a cylinder with an internal cavity that is open at one end, into which different PTOs may be inserted) designed to interface with, support, and provide power to different PTOs, including PTOs of different sizes (e.g., 13/8" and 13/4" PTOs). While able to receive and support different PTOs, the PTO port may also adjust power transmission characteristics based upon differences in the shapes or sizes of PTOs. In particular, the PTO port may be designed so that the speed of rotation (e.g., 540 RPM or 1000 RPM) of the output sleeve changes in dependence upon the shape or size of the PTO inserted therein.
Use of this type of PTO output system provides an operator with a great deal of flexibility in attaching various devices requiring different PTO standards to the agricultural vehicle (especially since the different PTOs are provided at the same physical location on the agricultural vehicle). It also provides special problems. First, implementation of this type of PTO system may require a set of supplementary parts and accessories to retain and support the different PTOs (in addition to the output sleeve) that must be added or removed by an operator as PTOs are interchanged. If the additional parts are too complicated, numerous, or physically unwieldy, they may limit the utility of this type of PTO system.
Further, since implements often place significant forces on the PTOs, there may be a tendency for the PTOs to be pulled out of the output sleeve or for undue stress to be placed upon other elements of the agricultural vehicle if these forces are communicated to the output sleeve. This may occur if, for example, the attached device is an implement that has been stored outdoors such that it has a soiled or rusted input shaft that does not smoothly slide on and off the PTO (and so communicates axial forces to the PTO). Additionally, since the different PTOs may have different diameters, lengths and shapes (and weights), the output sleeve may experience differing forces from the different PTOs. Further, to the extent the PTOs are of different lengths, the output sleeve may experience significantly different torques as varying devices are attached to the PTOs.
Also, because more than one PTO of more than one standard is implemented at one port, and because it may be appropriate for the PTO output system to act differently upon different PTOs (e.g., it may be appropriate to deliver less torque to smaller PTOs than to larger PTOs due to the lower maximum torque that smaller PTOs may bear), obtaining information as to which PTO is currently in use in the output sleeve becomes valuable.
Accordingly, it would be advantageous to have a PTO output system that was able to accommodate various interchangeable PTOs and yet provide for quick, easy replacement of one PTO with another. It would also be advantageous to provide a PTO system that securely retained the PTOs within the PTO port. It would further be advantageous to provide proper support for the PTOs and to limit the transfer of force to elements internal to the agricultural vehicle in such a way as to avoid damage to those internal elements.